In the related art, linear predictive coding has been applied to encode a speech signal and an audio signal. A code excited linear prediction (CELP) coding technology has been employed for linear prediction. The CELP coding technology may use an excitation signal and a linear predictive coding (LPC) coefficient with respect to an input signal. When coding the input signal, the LPC coefficient may be quantized. However, quantizing of the LPC may have a narrowing dynamic range and may have difficulty in verifying a stability.
In addition, a codebook index for reconstructing an input signal may be selected in a decoding stage. When all the LPC coefficients are quantized with the same significance, deterioration may occur in a quality of a finally synthesized input signal. That is, since all the LPC coefficients have a different significance, a quality of the input signal may be enhanced when an error of an important LPC coefficient is small. However, when the quantization is performed by applying the same significance without considering that the LPC coefficients have a different significance, the quality of the input signal may be deteriorated.
Accordingly, there is a need for a method that may effectively quantize an LPC coefficient and may enhance a quality of a synthesized signal when reconstructing an input signal using a decoder. In addition, there is a desire for a technology that may have an excellent coding performance in a similar complexity.